IFN-alpha is a pleiotropic cytokine possessing immunomodulatory properties that may improve the efficacy of therapeutic cancer vaccines. The aim of this study was to evaluate the effectiveness and compatibility of combining recombinant IFN-alpha with poxvirus vaccines targeting the human carcinoembryonic antigen (CEA) in murine models of colorectal and pancreatic adenocarcinomas, where CEA is a self-antigen. The phenotypic and functional effects of IFN-alpha were evaluated in the draining inguinal lymph nodes of tumor-free mice. We studied the effect of the site of IFN-alpha administration (local versus distal) on antigen-specific immune responses to poxvirus vaccination. Mechanistic studies were conducted to assess the efficacy of IFN-alpha and CEA-directed poxvirus vaccines in tumor-bearing CEA transgenic mice. We identified a dose and schedule of IFN-alpha that induced a locoregional expansion of the draining inguinal lymph nodes and improved cellular cytotoxicity (natural killer and CD8+) and antigen presentation. Suppression of the vaccinia virus was avoided by administering IFN-alpha distal to the site of vaccination. The combination of IFN-alpha and vaccine inhibited tumor growth, improved survival, and elicited CEA-specific CTL responses in mice with CEA+ adenocarcinomas. In mice with pancreatic tumors, IFN-alpha slowed tumor growth, induced CTL activity, and increased CD8+ tumor-infiltrating lymphocytes. These data suggest that IFN-alpha can be used as a biological response modifier with antigen-directed poxvirus vaccines to yield significant therapeutic antitumor immune responses. This study provides the rationale and mechanistic insights to support a clinical trial of this immunotherapeutic strategy in patients with CEA-expressing carcinomas.